possibly, but start with basics, air filter ,plugs,tyre pressure's, brakes binding, air leaks,thermostat,fuel injection temp sensor, the list can be quiet exstensive but throwing a set of injectors at it is not only exspensive but a waste of time and money if the basic's have not been checked, of course if all other avenues have been exhausted then try a cleaner first,monitor it for awhile after, then try a set, but i have never in my lifetime of working on cars have ever changed a set (the odd failed one yes but not a set) Regards TB

vectra 2.0ltrs were never frugal unlike the cavalier. 25-26 local & 37 on a run 44 tops if your very light footed. make sure thermostat is functioning so engine is warming up quickly & make sure exhaust doesn't have a leak! even a small one will make it run richer. As Andrew has already pointed out where you buy your fuel can have quite an effect on economey & state of the injectors. With injectors ultrasonically cleaned may improve 2-3 mpg but no massive difference on these engines.
I can remember changing my 92 SRI130 cavalier for a vectra 98 SRi 140 & fuel consumption & performance were both very disappointing!

i tend to use tesco or sainsburys but i have heard that there fuels are not as good as say bp or shell but y ?? ive had it serviced but where is the injection temp sensor ? and how would i know if its working ok ? at the mo im only getting at best about 16 mpg and on a good run about 22 mpg. also the engine is burning oil about 1.5lr per 1000 mile and im getting to the stage where i may just get another car or a recon engine.

Keep it simple. Can your garage do a live data check on the coolant sensor to make sure that its giving the correct readings to the ECU & have an emmissions test carried out..2nd, doesthe temp gauge rise up to normal within a few minuets or does it take a long time ?
Try another make of fuel & put a bottle of injection cleaner in the tank.They can burn up to a ltr per 1k of oil anyway but with the amount of oil its burning it may well be reducing the effiency of the oxy sensor & cat.
Have you actually brimmed the tank & refilled to do a milage check? 16-22 is very poor & you would notice somethings wrong! the cat would stink

i will fill up next time at say bp. when i first start the car i get a smell of fumes in the cabin but after a few mins its gone. i also have wot i think is wet oil on the back box exit pipe but it could be petrol. i have done a mileage check and at best was only 22mpg.

Fumes in the cabin is not normal! For starters lift up the back seat cushion andd check for splits / loose connections around the fuel pump, accessed through the small circular panel under the seat. FWIW my 156K '99 2 litre - not sri - does 33 mpg around town and 43-44 on a run, mind you I do drive like a granny.